Variable capacitor



July 21, 1942 l G. l.. SSELMAN Erm. 2,290,508

VAR IABLE CAPAC ITOR Filed June 27., 19259 r/ 1111l.. w

1111/1/11/ vll Y 4 i gmmxmmw fla/im 3 7 INVENToRs GEORGE L. USSEL MAN BY A ATTORNEY.

Patente-d Juiy 21, 1942 VARIABLE CAPACITOR George L. Usselman, Port Jefferson, and Ralph E.

Franklin, Patchogue, N. Y., assignors to Radio Corporation of America, a. corporation o'f Delaware Application .fune 27, 1939, Serial No. 281,344

(Cl. F75-41.5)

8 Claims.

This invention relates to a new and novel variable condenser, and is similar in scope to a Vernier variable condenser described in the Franklin and Thorne patent application, iiled June 28, 1939, S. N. 281,642, except that instead of the movable electrode being of metal1 both electrodes are fixed and the condenser capacity ischanged by movement of a solid dielectric member which is interposed between two fixed electrodes, the variable feature being the change in the amount of dielectric between xed electrodes.

An object ci this invention is to simplify and improve adjustable variable capacitors for frequency measuring sets and similar apparatus.

Another object of this invention is to improve the type of variable condenser known in the prior art having a micrometer head for moving the variable'element with a suitable index therefor.

Still another object of this invention is to provide a variable Vernier condenser whose capacity remains substantially constant regardless of temperature changes, which is accomplished by the use o special materials having a low coecient of thermal expansion.

A feature of this invention is the arrangement oi the ordinary micrometer head with two iixed electrodes and a variable dielectric element.

This invention will best be understood by referring to the accompanying drawing, in which:

Fig. 1 is a longitudinal section of one embodiment of this invention;

Fig. 2 is a longitudinal section of another bodiment of this invention; and

Fig. 3 is a partial section of a modification of the embodiment shown in Fig. 1.

Referring now in detail to Fig. l of the drawlng, the condenser-of this invention comprises an outer cylindrical electrode lmade preferably of Invar or other simiiar metal of low coefiicient of thermal expansion. 2 is another lixed electrode in the form of arod which is supported from electrode i by means of an insulator t by screws 2a. Member i is secured to electrode i by screws a. A cylinder ci insulating material, such as fused quartz, is secured to and rotates with one end of a mieren ter 5 by ci a screw 5a which passes thru-ugh a metal sleeve 8 and forms the variable element. Micrometer head 5 is of the well- 'down machinists type of micrometer having a barrel which rotates on a thiinble with a spindle to which member 3 is the barrel having an internal thread .urns perv inch and turning on a threaded nut or thimble which haslocated on its outside surface circumferential divisions from l to 10 spaced apart from each other every tenth of an inch. These divisions are :further subdivided in four equal parts. The barrel portion of micrometer 5 has its outer periphery divided in twentynve divisions in order that one turn will `represent twenty-five thousandths of an inch on a horizontal index, located just above the subdivisions on the thimble. The condenser capacity is varied by movement of the outer barrel which in turn moves the solid dielectric variable element 3 in and out oi mesh between electrodes I and 2. A yoke 6 is provided for mounting the micrometer head and positioning member 3 concentric with electrodes l and 2 on a-panel l of insulatingA material by means of screws 6a which mounts the entire capacitor in any suitable position. Electrode l is secured to panel 'i' by means of screws la or, if desired, screws 6a may be extended to pass through both members 6 and i to serve as a common mounting means. .Electrical connection is made to electrode l by means of a terminal 9 and also a terminal l0 is provided for making connection to inner electrode 2. In this form of condenser, any small eccentricity in the mounting of electrode 2 within cas-` ing electrode l will not cause a variation in the rate of capacity change when changing the position of the solid dielectric 3 by means of rotating the micrometer head If the variable or solid dielectric member 3 is made of fused quartz or other material of a high dielectric constant, the condenser can be made much smaller for the same capacity than similar types of capacitors using air as the dielectric.

Referring new to Fig.l 2, the construction is somewhat modified but is generally similar to the structural arrangement of Fig. 1,'except for reasons of economy in cost and space require- `merit. As shown by the drawing, an electrode 22 is carried by the cylindrical insulator 23. The arrangement of being secured te micrometer head 5 is similar to that of Fig. l.. The outer electrode 2l, however, does not require the use of a supporting insulator but is' left open to receive a flexible lead -24 which is fastened te electrode 22 by means of a screw 25. Electrical connectionsare made to the electrodes by means of terminals Z6 and 2E.

As shown by Fig. 3 of the drawing, electrode i and insulator 43 may be combined as cne piece and constructed of insulation of fused quartz or y molded ceramic material. Electrode 33t is formed on the inner cylindrical surface of the insulator 34 which is disposed by chemical means, as by evaporation in a vacuum. Electrode 32 is also in the form of va coated metallic lm located on the cylindrical extension portion of member 34, suitable connections being made to the coated lm by means of a wire 35 passing through the upper wall of insulator 34 and soldered to coating 3l. Likewise, electric connection is made to coating 32 in a similar manner by means o a wire 36 passing through the central portion of insulator 34.

In all the above embodiments of the condenser, the interposed dielectric material should more nearly fill the space between the electrodes when the condenser is set for the maximum capacity position than is shown in the drawing, the larger spaces being indicated merely for the purpose of clarity.

Although only a few embodiments cf this invention are described, it is to be distinctly understood that it should not be limited to the precise arrangement shown.

What is claimed is:

l. A variable condenser of the solid dielectric type comprising a metallic casing acting as one electrode, an insulator secured to and forming one end of said casing, a second electrode secured to said insulator, a solid dielectric member interposed between said electrodes, and means to move the position of said solid dielectric member to change the capacity of said condenser.

2. A variable condenser of the solid dielectric type comprising a metallic casing acting as one electrode, an insulator secured to and forming vone end of said casing, a second electrode secured to said insulator, a solid dielectric member of fused quartz interposed between said electrodes, and means to move the position of said so'lid dielectric member to change the capacity of saidv condenser.

3. A variable condenser comprising a metallic casing acting as one electrode of said condenser,

4. A variable condenser of the solid dielectric I type comprising a metallic casing acting as one electrode, an insulator secured to andy orming 'one end of said casing, a second electrode secured to said insulator, a solid dielectric member interposed between said electrodes, and means to move the position of said solid dielectric to change the capacity of said condenser, said means comprising a threaded member secured to and rotating with said solid dielectric.

5. A variable condenser of the solid dielectric type comprising a metallic casing acting as one electrode, said casing secured to a panel mounting member, an insulator secured to and forming one end of said casing, a second electrode se cured to said insulator, a solid dielectric member interposed between said electrodes, and means to move the position of said solid dielectric to change the capacity of said condenser, said means comprising a yoke having supported thereto a threaded member which is arranged to rotate with said solid dielectric.

6. A variable condenser comprising a cylindrical metallic casing acting as one electrode of said condenser, a disc-like insulator secured to condenser, a disc-like insulator secured to an disc-like insulating member supported from the other electrode for securing said rod-like metallic member thereto, a solid dielectric member interposed between said electrodes, and means to move said solid dielectric to change the capacity of said condenser.

GEORGE-L. USSEIMAN.

H E. fui-1, xl N. 

